Hadith 500980
Chapter 2: Purity - كتاب الطهارة
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، أَنَّهُ كَانَ يَقُولُ مِنْ قُبْلَةِ الرَّجُلِ امْرَأَتَهُ الْوُضُوءُ . قَالَ { ابْنُ } نَافِعٍ قَالَ مَالِكٌ وَذَلِكَ أَحَبُّ مَا سَمِعْتُ إِلَىَّ .
Yahya related to me from Malik that Ibn Shihab used to say, "Wudu is necessary if a man kisses his wife." Nafi said that Malik said, "That is what I like most out of what I have heard."
Reference Muwatta Malik 500980
USC-MSA web (English) reference : Book 2, Hadith 68